# Transformer function and technical parameters

Transformer function and technical parameters

effect

A transformer is a stationary electrical device. It is a device that converts a certain level of AC voltage and current into another level of voltage and current of the same frequency according to the principle of electromagnetic induction. Function: Transform AC voltage, exchange AC current and transform impedance.

Technical Parameters

There are corresponding technical requirements for different types of transformers, which can be expressed by corresponding technical parameters. For example, the main technical parameters of the power transformer are: rated power, rated voltage and voltage ratio, rated frequency, operating temperature level, temperature rise, voltage regulation, insulation performance and moisture resistance. The main technical parameters for general low-frequency transformers are: transformation ratio, frequency characteristics, nonlinear distortion, magnetic shielding and electrostatic shielding, and efficiency.

Voltage ratio:

The number of turns of the two sets of transformers is N1 and N2, N1 is the primary and N2 is the secondary. An alternating voltage is applied to the primary coil, and an induced electromotive force is generated across the secondary coil. When N2>N1, its induced electromotive force is higher than the voltage applied by the primary. This transformer is called a step-up transformer; when N2<N1, its induced electromotive force is lower than the voltage applied by the primary. It is called a step-down transformer.

n=N1/N2

Where n is called the voltage ratio (turn ratio). When n>1, then N1>N2, U1>U2, the transformer is a step-down transformer. The reverse is the step-up transformer.

Transformer efficiency:

At rated power, the ratio of the output power of the transformer to the input power is called the efficiency of the transformer, ie

Where η is the efficiency of the transformer; P1 is the input power and P2 is the output power.

When the output power P2 of the transformer is equal to the input power P1, the efficiency η is equal to 100% and the transformer will not produce any losses. But in fact this kind of transformer is not available. Losses are always generated when the transformer transmits electrical energy. This loss mainly includes copper loss and iron loss. Copper loss is the loss caused by the resistance of the transformer coil. When current is generated by the coil resistance, a portion of the electrical energy is converted into thermal energy and lost. Since the coil is generally wound by an insulated copper wire, it is called a copper loss.

The iron loss of the transformer includes two aspects. The first is the hysteresis loss. When the alternating current passes through the transformer, the direction and magnitude of the magnetic field lines passing through the transformer silicon steel sheet change, so that the internal molecules of the silicon steel sheet rub against each other, releasing heat energy, thereby losing a part of the electric energy, which is the hysteresis loss. . The other is eddy current loss when the transformer is working. The magnetic core has a magnetic flux passing through it, and an induced current is generated on a plane perpendicular to the magnetic line. Since this current forms a circulating current from the closed loop and is spiral, it is called eddy current. The presence of eddy currents causes the core to heat up and consume energy. This loss is called eddy current loss.

The efficiency of the transformer is closely related to the power level of the transformer. Generally, the higher the power, the smaller the ratio of loss to output power, and the higher the efficiency. Conversely, the lower the power, the lower the efficiency.